detector alignment

Stefania and Bepo

Martellotti 20/12/10

Detector misalignment / Trigger inefficiency

- We know that hardware alignment is already good at the order of 1 mm. Is some further improvement possible ?

- Check alignment using trigger unbiased muons matched to high momentum tracks with a stand alone method independent of the tracking system alignment and independent of the geometry data base

We concentrate on misalignments affecting Trigger efficiency.Main effect is given by y misalignment of stations M1 M2 M3(Y FOI is only 1 pad while for M4 M5 is 3 pads)The effect of eventual x misalignments is less relevant and strongly “analysis/channel dependent”

Trigger efficiency - Y misalignments

Stefania muon meeting 23-04-2010

In the Y intercept of fitted track with plane Z=0 we see a spike of tracks with all Y pads perfectly aligned and many tracks with not aligned pads trigger inefficiency

1 m

Trigger inefficiency for

Multiple scattering Punch through Decays with large kink

& Detector misalignments

FOLLOWED PROCEDURE:

# Min Bias events# Muon ID with a) Neural Network algorithm b) “alessia algorithm” (starting from M5) same results have been obtained# Select muon tracks with hits in ≥ 4 stations# Select muons matched to high momentum long tracks

(different cuts on momentum have been tested)# Consider only events having one cluster per station

associated to the track. The cluster must be composed of (≤ 4) hits having the same Y # Start from the hit pad of station M2 # Consider the projective track IP-hitM2 (do not fit θYZ) and find the extrapolation in M1, M3

# Look in Mi at the difference between the Y of the cluster and the extrapolation from M2 ΔMi = YMi – YMiM2 # For tracks crossing the same region in the 3 stations ΔMi = 0 good alignment ΔMi = ± 1 pad physical misalignment (Mult Scatt…) or detector misalignment If Δ ≠ 0 for 1 station no L0mu trigger The purpose is to maximize trigger efficiency

ExampleYM2-YM3 DY = ± ½ pad

When tracks change region

DY = ± 1 padMult Scatt ormisalignment

Stefania

R1 R2 R3 R4

R1 R2 R3 R4Y

X

M3

M1

WITH MAGNET ON, TRACKS OFTEN CHANGE REGION

A track in M1R3can easily go in M3R4rarely in M3R2n X

Z

M3

M1

R3 R4R2

YM1-YM3 = ± 1/4pad ± 1/2pad rare frequent

Y station alignment w.r.t. M3 when track change region

M3 M3M1 M1

R2 R3

Count the Number ofDY = ± 1 pad Mult Scatt or misalignment

YM1-YM3

n+1

Misalignment can be measured by(n+1 - n-1)

Stefania

R2 R3

n-1

Supposing a uniform track distribution in the detector,we can assume that physical effects (MS, K decay kink, secondary interactions) smear symmetrically the distribution equally populating n+1 and n-1

Asymmetries can only be generated by detector misalignment that can be measured in each region multiplying the pad length by (n+1 - n-1) / (n0 + n +1 + n-1)

The hit distributions in Y are not at all uniform and generate systematic effects. Nevertheless the distributions are symmetric up and down considering side A/C as a whole the asymmetry (n+1 - n-1) should correctly measure the misalignment

No significant effects were detected eliminating border pads in regions R1 R2Viceversa systematic effects due to the non uniform muon/hit distributions have been observed looking at Up and Down quadrants separately:Significant systematic asymmetries are observed which do not correspond to real misalignments from the perfect projectivity. The relevance of these effects increases with low momenta (larger MS smearing) and for larger pad size. Such effects have been studied with MC

We have measured misalignments considering sides A-C as a whole.But also checked separately different regions and different quadrants and eventually considered only tracks crossing M3 in the inner pads of the chambers in regions R1, R2 to check possible systematic effects at chamber edges

R1 +R2

R125mm

R250mm

ΔY

St//Re A-side (y<0- y>0)/2 C-side (y<0- y>0)/2

M1R125mm

1.21±0.13 (0.97) 0.889±0.13 (1.5)

M1R2

50mm 1.21±0.19 (2.9) 0.543±0.19 (2.5)

M3R134mm

0.414±0.095 (-0.93) 0.37±0.095 (-0.68)

M3R268mm

0.526±0.11 (-2.1) 0.673±0.11 (-2.1)

Misalignments found (for MB data) in mm ± statistical error (systematic difference Up/Down)

Residuals for y>0 and y<0 have opposite signs - The effect is due to non uniformity of the hit distribution, Multiple scattering & large pad size- The effecrt increase with the region, decrease with high momentum tracks- The average (y>0 + y<0) should measure the deviation from projectivity due to relative misalignments. - The pattern on M1 is reversed respect M3 since M2 is taken as reference for projectivity- The results obtained for R1 and R2 are averaged

SHIFTS TO BE APPLIED To correct misalignment (mm) ± statistical error

M1 M2 M3

A 1.2 ±0.11 0 0.45 ±0.08

C 0.75 ±0.11 0 0.5 ±0.08

Alternatively we can shift M2 and M3

Y

C 0 -0.75 -0.25

A 0 -1.2 -0.75

Station/Region

A-side Systematics C-side Systematics

M1R125mm

0.437±0.21 1.6 mm 1.14±0.22 1.3 mm

M1R250mm

0.398±0.31 3.3 mm 1.2±0.32 2.8 mm

M3R134mm

0.379±0.16 1.6 mm 0.136±0.16 1 mm

M3R268mm

0.302±0.18 2.3 mm 0.109±0.19 1.9 mm

• MC2010 MBias• Nnet track selection• Applied the same cuts of the real data• In the table are counts for 0 - + 1 pad

MisalignmentsMCarlo MBias

•MC shows same pattern as real data.•The mean value (y>0 + y<0) should return the simulated deviations from projectivity that was in the DDDB+LHCBCOND DDDB: head-20100407 ---> Survey (see DATA BASE INFORMATION)

values respect “nominal” (TDR) positionsNB: C side is rotated by 180º respect Aside:

Dz >0 means more downstream for ABut more upstream for C-side

Dx >0 means far from beam pipe for Aside BUT closer to the beam pipe for C-side

DDDB C-side A-side[mm] Tx Ty Tz Ry [o] Tx Ty Tz Ry [o]M1 -4.8 -1.2 4.3 -0.11 6.2 -1.0 6.8 0.03M2 -8.7 0 -10.7 0 8.6 0 -8.8 0.06M3 -9.7 0 -6.3 0 9.6 0 -1.7 0.04M4 -11.6 0 -13.4 0 11.8 0 -7.9 -0.04M5 -11.6 0 -5.4 0.05 13.0 0 0.8 0.09

Station/Region

A-side systematics C-side systematics

M1R125mm

0.302±0.065 0.044 0.903±0.065 0.026

M1R250mm

0.859±0.1 0.18 0.781±0.1 0.056

M3R134mm

0.0515±0.057 0.24 -0.019±0.056 0.26

M3R268mm

0.015±0.089 0.5 0.033±0.085 0.45

Mcarlo Jpsi Systematics are much smaller than for Mbias ==> they are due to multiple scattering

ConclusionThe method is robust – Independent of eventual misalignments of tracking system and of Data Base There are still misalignments of the order of 1 mm in the detector# Shall we (can we) correct them ?MC studies confirm that we understand systematics - Summing quadrants Up and Down, systematic effects are almost cancelled (possible residual systematic effect on the result are certainly small)Some further check could be done in the next days in particular increasing the statistic of real data and selecting higher momenta.

General comment:Trigger : too small YFOI in M1 M2 we loose significantly efficiency

SPARES

RealData MBias• Apr2010 Mbias data• Nnet track selection• Applied the same cuts of the real data• In the table are counts for 0 - + 1 pad

RealData MBias

Mcarlo MBias

• MC2010 MBias• Nnet track selection• Applied the same

cuts of the real data• In the table are

counts for 0 - + 1 pad

Trigger algorithm in few words:

Starting from each M3 seed, look for hits in the other stations

- Search in projective XY FOI in M4, M5 (± 1 pad Y allowed) - Search in projective FOI in M2 (only one pad Y allowed)- Make the straight line M3M2 (seed – hit found)

From here on two possibilities with or without M1

M1 yes: open FOI in M1 around M3M2 extrap. (only one pad Y) find the nearest hit to the extrapolation

make the straight line M2M1M1 no: use directly the M3 M2 straight line

calculate pT cut

Alessia 19/05/2010Monte Carlo